As night activities are becoming more common and that better technologies are being developed such that different properties of lighting apparatus are required, such as broad-beamed, high intensity floodlight for nighttime luminance and coherent, more variations of lighting apparatus are being developed for different purposes. LED may be used in a wide range of applications due to its low-cost, high energy efficiency. For example, it may be used as headlights or flashlights. LED may also be used as backlights in display panels.
Despite a high energy efficiency of LED lighting, a considerable amount of photons are still lost to the surroundings, or say the escape cone, due to the refractive properties of the medium. Due to total internal refraction, which is the reflection of photons upon entering a different medium with a lower refractive index, these reflected photons do not contribute to the desired illumination which the LED provides.
Patterned sapphire substrate (PSS) technique may be employed to improve the luminosity and light extraction efficiency. By applying a nano-array of structures on the photon escaping interface between the two mediums, i.e. sapphire and air, more photons may be extracted from the escape cone than from a flat surface, achieving an overall brighter LED.